A machining center, which commonly comprises a machine tool, a tool storage station and a tool exchanging mechanism, is known to be highly efficient and versatile and useful for shaping a workpiece with an intricate contour by utilizing a plurality of formed machining tools which are simpler but different in shape, or which are similar to each other but different in size. These tools are preformed and introduced into the system by a magazine in the tool storage station. The tool exchanging mechanism is operated under numerical control to select the stored tools in a programmed order and to transfer each selected tool to and secure the tool in a tool holder in the machine tool. The machine tool, which may be an electroerosion machine, is also typically operated under full numerical commands to machine a workpiece into a predetermined surface and precision grade or partial shaping pattern pre-alotted therein. The tool exchanging mechanism then unloads the selected working tool from the machine tool and returns it to the storage station for exchange with a new selected working tool to transfer the latter to the machine tool for a subsequent machining operation. It is also possible to use a different tool stored in the magazine for a different workpiece loaded in the machine tool.
In certain types of machine tools such as electroerosion machine, it is known that a formed machining tool wears quickly. Thus, for a given shaping purpose it may be vital that a number of tools (electrodes) of precisely identical form and size be prepared. Also, for the sake of machining efficiency there may arise a need for successive machining grades of tools which are similar but of slightly different sizes. These tools or electrodes must each be preformed with precision but once used become inaccurate due to wear. In the existing machining centers, therefore, the worn tools have been nothing other than scraps or the equivalent which can after return to the storage magazine be simply discarded or removed as being no longer useful therein.
It should also be pointed out that a numerically controlled machine tool, e.g. electroerosion machine, has the ability to position each machining tool therein for and during a given machining operation and the ability to achieve a machined shape unparalleled and yet accurately predictable precision. The ability to precision-position the working tool in the numerical control system is, however, limited to the positioning of a tool center or reference point in its coordinate system. If there is any inaccuracy in the position of each point of the preformed machining tool which is introduced into and maintained in the system, the machining accuracy is far less than the genuine precision thereof. In the existing machining centers, it has been found that such an inaccuracy is at least one order greater than the true inaccuracy of a given NC system for use on the commercial scale.